The present invention concerns aircraft structures.
More particularly, but not exclusively, this invention concerns an aircraft structure comprising a joint between two sub-structures, in particular between two sections of wing. The invention also concerns an aircraft comprising such an aircraft structure and a method of manufacturing an aircraft structure.
There are many different known ways of connecting two wing sections together. For example, a full tension fitting arrangement can be used to connect two wing box sections together or to attach a wing tip to a wing box. Such an arrangement is a quick way of connecting the two sub-structures together but has a weight penalty, as the tensioning arrangement is relatively heavy.
Another way of attaching two wing sections together involves having a cruciform structure in between an outer wing box and a centre wing box on the upper cover and having a triform structure in between the two wing boxes on the lower cover. These are shown in FIGS. 1a and 1b, respectively.
In FIG. 1a, it can be seen that a generally upright portion 11 of the cruciform structure 10 is connected to a shared rib 20 of both wing boxes 30, 40. A first generally horizontal portion 12 of the cruciform structure is attached to the upper cover 37 of the outer wing box 30 and to a stringer flange 31a of a stringer 31 of the outer wing box 30 by bolts 33 (a to d, although not individually labelled). A second generally horizontal portion 13 of the cruciform structure 10 is attached to a stringer flange 41a of a stringer 41 of the centre wing box 40 again by bolts 43 (a to d, although not individually labelled). There are also additional crown fittings 32, 42 used to spread the load between the cruciform structure 10 and the stringers 31, 41 of both wing boxes 30, 40. The crown fittings 32, 42 are attached to the shared rib 20 and cruciform structure 10 by a tension bolt 21 extending through the shared rib 20, generally upright portion 11 of the cruciform structure 10 and crown fitting flanges 32a, 42a of the crown fittings 32, 42. The crown fittings 32, 42 are attached to the stringers 31, 41 of both wing boxes by fasteners 34, 44 through blades 32b, 42b of the crown fittings 32, 42 and stringer blades 31b, 41b of the stringers 31, 41.
In FIG. 1b it can be seen that a generally upright portion 51 of the triform structure 50 is attached to the shared rib 20 by a bolt 22. Two generally horizontal portions 52, 53 of the triform structure 50 are also attached to stringer flanges 35a, 45a of stringers 35, 45 of both wing boxes 30, 40 by bolts 36a, 36b, 36c, 36d, 46a, 46b, 46c, 46d. In addition, a splice plate 23 (also known as a buttstrap) connects the two stringers 35. 45. It is also held in place by some of the same bolts 36b, 36c, 36d, 46a, 46b, 46c attaching the stringer flanges 35a, 45a to the triform structure 50.
Having a cruciform and triform structure to connect two wig boxes allows the two wing boxes to be able to be completed separately. However, it also means that the joining procedure is relatively complex and requires significant fettling and shimming to meet the required tolerances. This takes a significant amount of time to do. In addition, a large number of parts are involved, which adds to the costs and weight of the aircraft.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved aircraft structure, an improved aircraft and an improved method of manufacturing an aircraft structure.